Lower 2HG levels may be found in lower grade gliomas and with low tumor cellularity regardless of glioma grade.11,26 Transformation from low-grade to high-grade glioma is associated with significantly increased tumor volume, a marked increase in tumor cellularity and MIB-1 proliferation index, as well as up to three-fold increase in 2HG levels. This evidence concerns the gene MIB1 and central nervous system cancer.